Field of the Invention
The present invention relates to a semiconductor device, a solid-state imaging device, and an imaging device which are formed by connecting a plurality of substrates with each other.
Description of Related Art
In recent years, video cameras, electronic still cameras, and the like have been widely circulated among the public. In such cameras, charge-coupled device (CCD)-type or amplification-type solid-state imaging devices are used. In such an amplification-type solid-state imaging device, signal charges generated by and accumulated in photoelectric conversion units of pixels which receive incident light are guided to amplification units provided in the pixels. Signals amplified by the amplification units are output from the pixels. In an amplification-type solid-state imaging device, a plurality of such pixels are arrayed in a two-dimensional matrix shape. Amplification-type solid-state imaging devices include, for example, complementary metal oxide semiconductor (CMOS)-type solid-state imaging devices which use CMOS transistors, and the like.
In the related art, a general CMOS-type solid-state imaging device employs a scheme in which signal charges generated by photoelectric conversion units of each of pixels arrayed in a two-dimensional matrix shape are sequentially read out for each row. In this scheme, since a timing of light exposure in the photoelectric conversion units of the pixels is decided based on a start and an end of readout of the signal charge, timings of light exposure are different in rows. For this reason, when a fast-moving subject is imaged using such a CMOS-type solid-state imaging device, the subject becomes distorted in a captured image.
In order to remove distortion of a subject, a simultaneous imaging function (global shutter function) which realizes simultaneity in accumulation of signal charges has been proposed. In addition, applications of CMOS-type solid-state imaging devices with the global shutter function are becoming diverse. A CMOS-type solid-state imaging device with the global shutter function generally needs to have an accumulation capacitor which has a light-shielding property to accumulate signal charges generated by photoelectric conversion units before the signal charges are read out. In such a CMOS-type solid-state imaging device of the related art, after all pixels are simultaneously exposed, signal charges generated by photoelectric conversion units are simultaneously transferred to accumulation capacitors in all of the pixels and temporarily accumulated for the moment. The accumulated signal charges are sequentially converted into pixel signals and read out at predetermined readout timings.
In a CMOS-type solid-state imaging device with the global shutter function of the related art, photoelectric conversion units and accumulation capacitors need to be created on the same plane of the same substrate, and thus the size of the substrate increases. Furthermore, during a waiting period before signal charges accumulated in the accumulation capacitors are read out, quality of signals deteriorates due to noise caused by light or noise caused by a leaking current (dark current) occurring in the accumulation capacitors.
Japanese Unexamined Patent Application, First Publication No. 2006-49361 discloses a solid-state imaging device to solve the above problems. This solid-state imaging device includes a MOS image sensor substrate on which micropads are formed on a wiring layer side for each unit cell and a signal-processing substrate on which micropads are formed on the wiring layer side at the position corresponding to the micropads of the MOS image sensor substrate. The MOS image sensor substrate and the signal-processing substrate are connected to each other by microbumps. In addition, Japanese Unexamined Patent Application, First Publication No. 2010-219339 discloses a method for preventing the area of a substrate from increasing. In this method, a solid-state imaging device, in which a first substrate on which a photoelectric conversion unit is formed and a second substrate on which a plurality of MOS transistors are formed are bonded, is used.
In a process in which two substrates (for example, the MOS image sensor substrate and the signal-processing substrate) constituting a semiconductor device such as a solid-state imaging device are connected using microbumps (which will be described hereinafter as bumps) or the like, there is a process of performing positioning of substrates (alignment) in order to prevent deviation during connection (alignment process). Each substrate has a mark that is called an alignment mark. For example, there is an alignment mark obtained by using a base electrode for forming a bump which connects substrates.